My windshield had sustained some damage (bullet hole) and was going to have to be replaced. After reading what people posted here about windshield replacement, I wanted to do it right and repair all the rust while I was in there.
To replace the windshield I went to a cheap corner window shop and asked them to just remove my windshield and tape it back on so I can drive home. Keep in mind, I knew they were going to use the jig-saw like tool that may cause paint damage (mentioned in this post on sprinter-source forum), but it didn't matter to me since I was going to be repairing it all.
Tapped it up enough to drive under a mile and get ready for the repairs.
The rust was really visible around the windshield once the gasket/seal was removed:
Next I took the windshield out and the hood off and covered the rest of the van and dash as best I could. Then the next step was to remove old rust. I really like using an angle grinder with sanding discs. They are aggressive, but great at getting down to bare metal.
While I had the hood off I went after the rust underneath the hood also.
Once all the rust is removed I did the three steps (mentioned above... clean, prep, paint) and applied POR-15 to the metal. I buy these little cans since I don't use a ton in one go and I feel like they keep better that way.
Once it was all done it looked pretty good, but keep in mind that POR-15 is not UV resistant so you need to coat it with some UV resistant paint. I used a factory matched paint then a clear coat... all rattle can. Does not look professional haha, but more than good enough for me.
After the paint was dried I called up the window replacement guy (done under insurance) and they showed up and installed it in the alley. I think he was presently surprised that the windshield was already removed :-)